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December 1940 




RECENT developments resulting from the advent of TECO modern timber connectors have 
radically improved the method of designing timber structures. New information con- 
stantly becoming available makes it practically impossible for even current engineering text- 
books to present adequately this information. For this reason the Timber Engineering Com- 
pany has prepared the following discussion and recommendations covering the fundamental 
principles of the improvements in timber design as they apply to the design and load data 
for TECO timber connectors given in the 1939 Manual of Timber Connector Construction. 


TECO Timber Connectors . . 

Types and Uses 

Plate I, Typical Connector Joints 

Design Information 

Description of Terms Relating to Connector Design 

Conditions Affecting Connector Loads 

Factors Influencing Connector Joint Design 

Procedure for the Design of Connector Joints 

Design of Structural Members 

Plate II, Fink Roof Truss, 50 Foot Span 

Design of Timber Joints 

Load Parallel to Grain 

Tension Joint 

Compression Joint 

Load at Angle to Grain 

Chord Members Between Web Members 

Chord Members Outside Web Members 

Heel Joint Fink Truss 

Peak Joint Fink Truss 

Design of Members with Combined Bending and Axial Loads 

Combined Axial Tension and Bending 

Columns with Combined End Load and Side Load 
Plate III. Permanent Grandstand 




• • • •• 
• • . • • 

^ » • • * I CojujTJght, 1940 

• • • 'I 'V •» •• 

•• ir» ' T'n»fc#r Engineering Company 

• • • 

• • • 



By J. E. Myer, Research Engineer* 


TECO timber connectors used in structural joints are 
metal devices employed in the contact faces of lapped 
members to transfer load from one member to another, 
the joint being held together by one or more bolts. One- 
half of the connector or connector unit is installed in 
each contact face and transfers load proportionately to 
the size of the connector. It is this large bearing area of 
the connector against the wood near the surface of the 
timber where the intensity of the stress is greatest as 
compared to the limited area under a bolt which accounts 
for the high efficiency which can be developed in timber 
joints with connectors. With connectors in the limited 
joint area it is now feasible to develop up to 100%' of 
the working stresses of the timbers. Such a high per- 
centage of load transfer with bolts or nails alone is either 
expensive or impractical. 

Split Ring Joint with Portion of One Member Cut Away to Show 
Position of Rings and Bolts 

Structural lumber of the smaller dimensions, readily 
available in local lumber yards, may now be used with 
connectors to exceptional advantage, and greater efficiency 
is possible for large timber sizes. Furthermore, the 
TECO system of construction eliminates much of the 
complicated framing of joints found in many of the 
timber structures designed before connectors were avail- 
able. Some of the important advantages of timber con- 
nector design are that timber designing is simplified, that 
more efficient use of lumber is provided and that less 
hardware is required, thereby resulting in more practical 
and more economical structures and frequently of designs 
hitherto thought of only in other structural materials. 

♦ Arknowleditment for \aIiiabU" assistante is niailf to nienih^rs ni th»* -.taff of 
ihe Forest I*roiiucts Laboratory, partirularly to J. A. Newlin ami J. A. Siholten. 


Efficient connections for either timber-to-timber joints 
or timber-to-steel joints are provided by the several types 
of TECO timber connectors. The most appropriate type 
for a specific structure is determined primarily by the 
kind of joints to be made and the load to be carried. 
The following brief description of the functions of the 
different connectors is offered to assist the designer in 
selecting the appropriate type or types of connectors for 
a structure. 

Fig. 1 — Split Ring 

Fig. 2 — Toothed Ring 

Split Rings (Fig. 1) and Toothrd Rings (Fig. 2) 
are two kinds of connectors used for limber-to-limlxT 
joints. Split rings carry greater loads and reccivt^ more 
common usage except in relatively light timber framing 
where toothed rings are adequate. Split rings are |)hi(<Hl 
in grooves cut into the contact faces of overlapped tim- 
i)ers with half the depth of the ring in the groove of each 
member. A power tool is recommended for cutting the 
grooves. No groove is required for installing toothed 
rings since these are embedded into the wood by j)ressurc 
developed by means of a high strength rod and ball-bear- 
ing washer assembly used along with a ratchet wrench 
or by other convenient means which may be at hand such 
as a power press. 

Fig. 3 Bearing Surfaces for Split Ring Connectors 

The purpose of the tongue and slot split in the cir- 
cumference of the ring is to permit simultaneous bear- 
ing against the core inside the ring and against the wood 
outside the ring. See shaded areas. Fig. 3. Due to the 
split in its perimeter, the ring is to some extent flexible 
in the direction of the load. The core inside the groove 
is cut larger than the diameter of a closed ring so that 




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when the ring is installed in the two grooves of two con- 
tacting timber faces it is sprung open and fits tightly 
against the two cores. With wood and steel already in 
contact at A and B, Fig. 3, load applied on the members 
causes these surfaces to come promptly into bearing. A 
slight slip in the joint also occurs due to the width of the 
groove which is cut a few thousandths inches larger than 
the thickness of the ring to facilitate its installation. As 
this slip occurs, the ring is slightly elongated and comes 
into bearing at C and D, thus permitting bearing against 
the wood both inside and outside the ring. 


Fig. 4 — Claw Plates 


Front Back 


Front Back 

Malleable Iron 

Fig. 5 — Shear Plates 

Claw Plates (Fig. 4) and Shear Plates (Fig. 5) 
each provide for timber-to-timber and timber-to-metal 
connections. In a timber-to-timber joint the following 
combinations of connectors may be used together, (1) one 
male and one female claw plate, (2) two female claw 
plates and (3) two flanged shear plates. In a timber-to- 
steel joint, all three kinds of plates may be used singly 
with the hole in the steel plate large enough to receive 
the hub of the male claw plate or the bolt to fit the female 
claw plate or shear plate. 

These plate connectors require pre-cut daps in the tim- 
bers to receive them. Shear plate daps accommodate the 
entire connector, but the teeth of the claw plates must be 
embedded into the wood below the limit of the dap. This 
can be accomplished by driving or by pressure. The 
teeth on the claw plates hold them quite securely in the 
timbers during erection. Shear plates are held in their 
daps by nails driven through the holes or slots in the 
plates for that purpose. When installed, the outer hub of 
the male claw plate protrudes from the surface of the 
limber in contrast with the female claw plate and shear 
plate which have their flat backs flush with the timber 
surface. The primary advantage of the connector being 
flush with the timber surface is that the assembly of cer- 
tain timber joints is permitted which would otherwise 
be impossible. The plates which fit flush with the timber 
surface are also more suitable for demountable struc- 
tures since the joints come apart more readily and there 

is less chance for the connectors to be pried out of their 
daps. The smaller amount of slip in claw plate joints 
as compared with shear plate joints may make the use 
of claw plates more desirable for some types of joints, 
especially where reversal of stresses may occur. 

Spike Grid connectors (Fig. 6) are designed for 
timber-to-timber joints in which the contact faces are 
either flat or curved. The flat grid is used to join two 
flat faces of lapped timbers; for example, timber braces 
to timber posts in trestle bents. The single curve grid 
is used to join a member with a flat surface to one with 
a curved surface, such as a timber brace to a round pile. 
The double curve grid is used to join two parallel mem- 
bers with curved surfaces, for example, two round piles. 
Spike grids are embedded into the timbers by pressure 
most conveniently developed by a high strength rod and 
ball-bearing washer assembly. These connectors give 
a high degree of rigidity to joints with an exceptionally 
small amount of deformation under working loads. 


Sinsle Curve 

Fig. 6 — Spike Grids 

Double Curve 

Plain Flanged 

Fig. 7 — Clamping Plates 

Clamping Plates (Fig. 7) are suited primarily for 
connecting timbers lapped at right angles, for example, 
as "tie spacers" for fastening ties to timber guard rails 
on open deck railroad trestles or bridges. The plain 
clamping plate makes a somewhat more rigid connection 
in that the teeth are embedded into both members whereas 
the flanged plate may permit a slight movement. On the 
other hand, the flanged plate permits greater ease in the 
replacement of ties. The installation of the plates re- 
quires that the teeth be embedded by means of driving. 
Plain clamping plates with teeth on two sides take two 
driving operations, one to get the teeth into the tie and 
another to get the teeth on the opposite face into the 
timber guard rail. The flanged clamping plate with teeth 
on one side requires only one driving operation, that of 
seating the teeth into the timber guard rail. 


The TECO system of construction follows the same 
general structural design procedure as other materials 



and methods. It is the simplification of the joints by 
using timber connectors which makes possible greater 
eflSciency in the use of lumber and ease of designing than 
heretofore. The necessary information required for this 
system of construction is given in the list of Supplements 
to Wood Structural Design Data published by the Na- 
tional Lumber Manufacturers Association: 

Supplement No. 1 Working Stresses for Structural 
Lumber and Timber 

Supplement No. 2 Bolted Wood Joints, Safe Loads on 
Common Bolts 

Supplement No. 4 Wood Columns, Safe Loads 

Supplement No. 5 — Wood Trusses, Strength Coef- 
ficients, Length Coefficients, and Angles. 

Supplement No. 6 Timber Connectors, Design and Load 
Data, also known as the "Manual of Timber Connector 
Construction" or the "Manual". 

These supplements are available on request either 
from the Association or from the Timber Engineering 
Company, a subsidiary, both concerns with addresses at 
1337 Connecticut Avenue, Washington, D. C. The fol- 
lowing description of terms, discussion of rules and ex- 
amples as they apply to connector construction are pre- 
sented to assist the designer in the application of this 
information to specific cases. 


The descriptions of terms used in the Manual are given 
as they pertain to timber connector design. 

Timber Connectors are metal devices employed in 
timber joints to transfer load from one member to another, 
the members being held together by one or more bolts. 

Standard Design Loads or working loads for con- 
nectors tabulated in the Manual apply to most of the 
loading conditions under which all types of TECO con- 
nectors are used where the dead load is less than the 
live load, and where the full live load is applied for 
relatively short periods of time, such as a snow load on 
a roof truss. Standard Design Loads are 1157c of basic 

Basic Values are derived by applying appropriate 
factors to test data. They allow for a permanently ap- 
plied full load, a condition not usually encountered in 
the use of timber connectors. 

Species Group is a classification given different struc- 
tural species of lumber based on the relative loads de- 
veloped by connectors in those species. 

The Compression Side of a connector is the outside 
portion of the connector which is in compression against 
the wood. 

Shear Area for a connector is considered as beinf^ 
equal to that area between the compression side of the con- 

nector and the edge or end of a member, or between two 
connectors and of a width equal to the diameter of the 
connector. (See Fig. 9-B.) 

Angle of Load to Grain is the angle formed by the 
direction of the load transmitted to a member by a con- 
nector and the direction of the grain in the member. 
(See Fig. 8.) 

OirccHon of Orain 
Fig. 8~Angle of Load to Grain 

End Distance is the distance measured parallel to the 
grain from the center of the connector to that point toward 
the end of the member which provides a shear area for 
the connector equal to that provided by an end cut square 
across the member the same distance from the center of 
the connector. 

Fig. 9-A — Method of Measuring Spacings and End Distances for 
Timber Connectors with Square or Single Diagonal End Cut 

a. Connector spacing parallel to grain 

b. Connector spacing perpendicular to grain 

c. End distance 

d. Edge distance 

e. Maintain end distance as minimum 

f. Maintain edge distance as minimum 


Fig. 9-B~-Tension Member with Two Diagonal End Cuts 

For the above case with the two diagonal cuts at 45^ the end 
distanc^e (e) is measured to a point equal to one^half the distance 
trom the end of the member to a line perpendicular to the axis of 
the member passing through the intersection of the diagonal cut 
and the Ime projected from the edge of the connector. 


End distance is measured from the center of the con- 
nector parallel to the grain to the end cut where this is 
square across the member or where a single diagonal cut 
extends across the full width of the projected diameter of 
the connector. If a single diagonal cut does not extend 
fully across the projected diameter of the connector, or 
if two diagonal cuts are made, the shear area must be 
determined to find the end distance. This can usually be 
estimated reasonably close for design purposes. (See 
Figs. 9-A and 9.B.) 

Edge Distance is the distance measured perpendicular 
to the grain from the center of the connector to the edge 
of the face of the piece into which the connector is in- 

Edge Distance on the Compression Side of the 
connector is measured from the center of the connector 
to the edge of the piece nearest the center of the compres- 
sion side of the connector. (See Fig. 10.) 

Edge Distance Opposite the Compression Side 
of the connector is measured from the center of the con- 
nector to the edge of the piece nearest the center of the 
outside portion of the connector not in compression 
against the wood. 

View £-£ 

/f/n^ in F/sce A 

Fig. 10 — Compression Side of Ring 

D — Edge distance on compression side of connector in piece A 
which is assumed to be held in place by forces not indicated. 

Spacing of Connectors is the distance between the 
centers of two connectors in the same timber face. Con- 
nectors are spaced either parallel or perpendicular to the 

Connectors are considered to be spaced parallel to the 
grain when a line drawn through the axes of connectors 
in the same timber face forms an angle less than 30^ 
with the direction of grain. Connectors are considered 
to be spaced perpendicular to the grain when a line 
drawn through the axes of connectors in the same timber 
face forms an angle of 30° or more with the direction 
of grain. 

Standard Spacings and Distances are those re- 
quired for full Standard Design Loads. Greater spacings 

or distances do not permit increases in connector capaci- 

Minimum Spacings and Distances are the smallest 
permitted for use with connectors and except where mini- 
mum and standard spacings and distances are the same, 
require reductions in connector loads as specified in the 

Cross- or Stitch-Bolt is a bolt located halfway from 
the edge of the connector to the end of a member, ex- 
tending in a direction parallel to the face in which the 
connector is located and at right angles to the grain. 
(See Fig. 11.) Its application to connector design is in 
tension members as it permits end distances for tension 
members to be equal to the lesser standard end distances 
for compression members and still carry full rated loads. 

Tension member 

hy Cros^ bo/r 

e = End distance for connector 

X = D/stance from connector fo end of piece 

Fig. 11 — Illustration Showing Use of Cross Bolt 


Angle of Load to Grain 

Wood has greater compression strength parallel with 
the grain than across the grain and, in general, the ca- 
pacities of connectors decrease as the angle of load to 
grain increases. It is important, therefore, to determine 
the member in which the load acts at an angle to grain. 
This may readily be determined for each member by con- 
sidering the forces acting and the relative position of the 
overlapped members in the joint. 

Fig. 12-A shows a two member joint with members 
entering at an angle 6. If the vertical component of 
diagonal member A is counteracted by reaction C then 
the direction of load on the connector in member B must 
be parallel to grain in this piece since the only force 
applied is axial. Member A. however, in addition to its 
axial load, has its vertical component counteracted by 
reaction C so that only the horizontal component remains. 


resulting in a load on connector in member A equal and 
opposite in direction to that in member B. It is this 
direction of load on the connector with reference to the 
direction of grain in each member which determines the 
angle of load to grain for each member. On the other 
hand, if horizontal member B is held in equilibrium by 
reaction C, then the direction of load on the connector in 
member B is at an angle of load to grain equal to 6 and 
the direction of load on the connector in member A is 
parallel to grain. From this it is apparent that a member 
loaded only axially bears on the connector in a direction 
parallel or 0° to the grain, also that a member with forces 
acting on it other than axial bears on the connector at an 
angle to grain. 

Fig. 12-A— Two Member Joint. See Discussion in Text. 

Assuming further that member A is supported by re- 
action C, and that member B has a superimposed load by 
the addition of ceiling joists spaced between panel points, 
then the direction of the load on the connector in member 
B is the resultant of the combined axial load and the 
reaction of the superimposed loads. The direction of this 
resultant and the direction of grain in each piece is used 
in determining the angles of load to grain in members 
A and B. 

An analysis of the three member joint in Fig. 12-B with 
three members entering the joint from different direc- 
tions shows that each of the two side pieces has only an 
axial load, while the center member has two forces acting 
on it, the vertical components of which counteract each 
other, similar to the vertical component of member A 
and its reaction C in Fig. 12-A. In this case, however, 
the forces are applied to connectors in the center member 
in the directions of the grain in the side members and the 
reactions in the center members are equal and opposite in 
direction. Therefore the angle of load to grain in the 
center member is determined by the angle formed by the 
center member and each side member. It will be noted 
that in a three member j oint it will normally be the center 
member in which the direction of load on the connector is 
at an angle to grain. 

Likewise in a joint with five overlapped members enter- 
ing from three directions, the second and fourth members, 
counting from one side to the other, are usually those 
loaded at an angle to the grain. 

Center member, B. Fig. 12-B, has the loads applied at an 
angle greater than 30° and toward opposite edges, a 
condition which requires that both edge distances must 
be equal to that specified for the compression side of 
the connector. The angle of load to grain is 0° in mem- 
bers A and C and, therefore, the capacity of the con- 
nectors in these pieces is greater than in member B. The 
load capacities for connectors are limited by the angle 
of load to grain in piece C, consequently end distances 
of members A and C may be reduced according to the 
percentage reduction allowed with reduced loads. 





£/VD V/EW 

Fig. 12-B — Three Member Joint with Load at Angle to Grain in 
Center Member; Load Parallel to Grain in Both Side Members 

End Distances and Connector Loads 

Full connector loads for 0° angle of load to grain re- 
quire standard end distances. Connector loads less than 
those for 0° angle of load to grain may take sub-standard 
end distances, or where sub-standard end distances are 
used, connector loads must be reduced proportionately. 
Permissible connector loads for sub-standard end dis- 
tances are determined by interpolation between standard 
and minimum values. For influence of a cross-bolt on 
end distance in tension members, see above. A cross-bolt 
placed in a member which is not seasoned to the extent 
It will reach in use should be tightened again after the 
member is thoroughly seasoned. 

Edge Distances and Connector Loads 

Full connector loads for the different angles of load to 
grain require standard edge distances. Where the angle 
of load to grain is less than 30°, the standard edge dis- 
tance is also the minimum edge distance and must be 
maintained. For an angle of load to grain greater than 
30 , the edge distance must be increased by the amount 
specified on the compression side of the connector to 
secure the rated load. If the edge distance is not in- 
creased as specified, when tiie angle of load to grain is 


greater than 30"^, the connector load is reduced; the 
maximum reduction being 15%. Permissible connector 
loads for sub-standard edge distances may be determined 
by interpolation between standard and minimum edge 
distances. The 30 degree angle for differentiating edge 
distances as well as for spacings discussed later, while 
based on tests, has been arbitrarily selected to present a 
convenient rule for the two general classes of loading, 
namely parallel and perpendicular to grain. It is to be 
expected that engineers in preparing designs, when 
necessary, w^ill exercise their judgment in arriving at 
what seems to be reasonable values in borderline cases 
around the 30° angle of load to grain. 

Spacing and Connector Loads 

Full connector loads for 0"^ angle of load to grain 
require standard spacings. With spacings less than 
standard, the design load capacity of the connectors in 
a row must be reduced. One connector in the row is 
excepted from the reduction in the convenient rule which 
has been devised for determining the reduction of load 
capacity for reduced spacing. This rule is based on test 
results and while not intended to designate the actual 
proportion of the total load carried by each connector 
in a row, it accomplishes the result of a proper reduc- 
tion of load for the row of connectors as a whole. The 
one connector in the row excepted from reduction in load 
capacity due to reduced spacing is considered, for the 
purpose of computing the total load capacity of the con- 
nectors, as carrying 100% of its rated load. For mini- 
mum spacing of connectors parallel to grain a 50% re- 
duction, and for minimum spacing perpendicular to 
grain a 15^^! reduction, applies to the load capacities for 
the balance of the connectors in the row. Reductions 
in connector loads due to angle of load to grain from 
0° to 30° may take reduced spacings to conform to the 
reduced loads. If spacings are reduced below this 
amount connector loads must then be reduced propor- 

Sub-Standard Distances, Sub-Standard Spacings 
and Connector Loads 

Connectors in a joint, in addition to sub-standard 
spacings, may have sub-standard end distances when the 
angle of load to grain is 0"^ — 30^; or they may have 
both sub-standard end and sub-standard edge distances 
when the angle of load to grain is 30^ — 90"^. To find 
the load capacity of a joint loaded 0°^ — 30° with two 
or more connectors spaced in a row with spacing and 
end distance both sub-standard, the procedures previously 
described apply; however, for convenience in computing 
the capacity of the joint it is assumed that the end con- 

nector is the connector which would carry 100% ca- 
pacity with full end distance, but since it has a sub- 
standard end distance this 100% capacity is reduced for 
the sub-standard end distance. This same principle of 
reduced loads for joints applies when angle of load to 
grain is 30° — 90°, but even though the end connector 
might have both sub-standard end distance as well as 
sub-standard edge distance, the reduction applied to the 
lOOVc capacity of the end connector is only the greater 
one of the two reductions. 

Spacing of Connectors in Members Overlapped 
at an Angle 

When two members come together to form a joint and 
the angle of load to grain is less than 30°, the con- 
nectors may be spaced with reference to the grain in 
either piece or in any intermediate position which may 
be convenient. Furthermore, if three members come to- 
gether to form a joint with the angle of load to grain less 
than 30^ for any two contacting members, as may be 
found in the peak joint of a Fink truss (See Fig. 13) 
with top chord B, web member A, and horizontal splice 
C, the connectors may be located with reference to any 
member and still develop the rated connector loads in 
each of these three members. 


Fig. 13 — A Three Member Joint with Each Two Contacting Mem- 
bers Forming an Angle of Load to Grain Less than 30^ 

Where the overlapped members of a joint enter at 
angles greater than 30°, the connectors must be spaced 
with reference to the member in which the angle of load 
to grain is greatest. If each of two overlapped members 
are loaded at an angle greater than 30"^ due to superim- 
posed loading, the connectors must have perpendicular 
to grain spacing, which is greater than the spacing paral- 
lel to grain; in this case the connectors may be spaced 
with reference to either member or adjusted to any posi- 
tion most suitable for the assembly of the joint. Fur- 
thermore if 85% or less of the rated load on the con- 
nectors is developed, the connectors may take the parallel 
to grain spacing. 


Wind, Earthquake, Net Section, etc. 

Other factors influencing connector loads are wind, 
earthquake, impact, lumber thickness, and condition of 
lumber. These factors and the required net section of 
a member in a connector joint are discussed in the Man- 
ual of Timber Connector Construction and are therefore 
not included here. 


Selection of Lumber Species and Sizes 

Lumber species selected for a structure will depend 
on the loads to be carried and the relative cost and avail- 
ability of the material. In large structures, where it is 
necessary to carry heavy loads, a structural species with 
relatively high working stresses and high connector work- 
ing loads will generally be found to be most satisfactory. 
However, if other considerations such as availability and 
cost of material are in favor of other species, these should 
also be considered. 

The TECO system, because of the required overlapped 
contact faces for placing connectors, utilizes to advantage 
thinner lumber than do other types of timber construc- 
tion. Another reason that thinner sections may be used 
economically and efficiently as compression members, is 
due to the fact that when the members are secured near 
their ends with connectors, the allowable load for a given 
l/d is increased according to the spaced column prin- 
ciple developed by the U. S. Forest Products Laboratory. 
(See Wood Structural Design Data Supplement No. 4, 
Wood Columns-Safe Loads.) The thickness of mem- 
bers should be selected with due consideration for the 
load to be carried, which involves the l/d ratio if the 
member is in compression, and for the overlapped area 
necessary to afford adequate end or edge distance and 
spacing for connectors. These limits will soon become 
apparent when proceeding to design a joint for a structure. 

Selection of Connector Type and Size 

The structure to be designed will quite definitely 
dictate the type or types of connectors to be selected. 
When (he joints involve only wood members, one of 
several tvpes of connectors might be used. However, 
since each connector is designed for a quite specific 
purpose as previously described, its efficiency is de- 
pendent on the type of connection and the amount of 
load to be carried. Timber-to-timber joints in structures 
carr\ing heavv loads may employ split rings, shear 
plates or claw plates. Split rings are used only in 
timber-to-limber joints since they must fit into grooves 
in the faces of the members joined; shear plates or 
female claw plates may be used in either timber-to-limber 

or timber-to-metal joint, because they lie flush with the 
surface of the member. Frequently, construction details 
are such that a member must be slid into place between 
other members or metal plates and it is this type of con- 
nection where the flush type of plate is required. 

In a structure designed for relatively heavy loads, 
where frequent dismantling is not anticipated, split 
rings will be found more appropriate than either shear 
plates or claw plates because of their lower cost. On 
the other hand, if a high percentage of the joints in the 
structure are of the wood-to-metal type, shear plates or 
claw plates are necessary in these joints to make an 
efficient connection. For this latter condition, rather 
than having two types of connectors in the structure with 
split rings for timber-to-timber joints and plate con- 
nectors for timber-to-metal joints, it may be desirable 
to use the plate type connector throughout. Should a 
proposed structure be of a type to be dismantled several 
times, such as an oil derrick, the shear plate connector 
will be found advantageous. These connectors are in- 
stalled flush in the timber and are held in place by 
nails. When the joints are taken apart there is no pos- 
sibility of impairing the strength of the joint by muti- 
lating the wood around the connector, and the flush 
plates provide for compact piling of members. 

Timber structures carrying relatively light loads and 
with thin structural members such as trussed rafters have 
employed toothed rings to very good advantage. No 
grooving is necessary and with templates for holding 
the members during assembly, toothed rings are in- 
stalled rapidly with the high strength rod and ball-bear- 
ing washer assembly or by means of presses rigged up 
on the job for the purpose. 

Another factor which may influence connector size is 
that frequently a single size is most efficient for nearly 
all the joints in a structure. Then, rather than specify 
two or more sizes, it is generally desirable to use the com- 
mon one for the remaining joints. Two or more sizes 
should not be avoided, however, where it is evident that 
a single size will not serve effectively and economically. 


For the convenience of those not already familiar with 
the customarv procedure employed in the design of 
timber joints, the following recommendations are offered. 
Wliile this procedure will apply to most structures, 
special cases may call for variations, but with the funda- 
mental steps in mind the variations can easily be made. 

1. Determine stresses for structural members. 

2. Form a tentative plan for framing the structure and 
select the lumber species to be used. 


3. Compute the sizes of the structural members. 

4. Select the type and size of connectors which seem to 
be most suitable for the structure. 

5. Determine the angle of load to grain for each mem- 
ber in the joint to get ring capacity, required edge 
and end distances and spacings for connectors. 

6. Design those joints first which carry the greatest 
loads, since the sizes of the members required to space 
the connectors in these joints will be a determining 
factor in arriving at final member sizes. 

7. Determine the amount of load in the joint which 
must be transferred between each two members to 
be joined and design for the largest load first; the 
positioning of the connectors for the smaller loads 
will usually not be a problem; they should, however, 
be checked. 

8. Compute the number of connectors required to carry 
the loads and proceed to locate them on gauge lines 
drawn with reference to the edges of the overlapped 
members. The spacings between connectors must 
also be checked, 

9. If gauge lines do not permit full spacings and full 
capacities of connectors must be developed, the face 
widths of certain members must then be increased 
to provide the spacings required, or it may be that 
other sizes of connectors can be used without in- 
creasing the lumber sizes. 

10. Check end distances and spacings for connectors in 
each member. 

An example illustrating the steps when designing 
structural members in a specific truss and the design of 
several typical joints will perhaps most clearly bring 
out the several fundamental principles previously dis- 
cussed. Their application to the design of other struc- 
tures and joints will be quite apparent. For this purpose 
a 50 foot Fink roof truss has been selected and a diagram 
for one-half of the truss with loads for each member is 
shown in Fig. 14, It is assumed that the roof loads are 
applied at the panel points. 

dS.40O^ ^'83^6," 30, 400 

Fig. 14— Diagram for One-half of 50 foot Fink Roof Truss Giving 
Loads for Members with Spacing of Trusses 16 feet on Centers 
and Combined Live and Dead Loads of 40 lbs. per Square J-oot 


Top Chord — Since the greatest load is developed in 
the top chord panels (see Supplement No. 5 Wood 
Trusses), the structural sizes should be designed for these 
loads first. To determine the size of the top chord in 
Fig. 14 it is assumed (1) that the chord will be composed 
of two members rather than one thereby providing greater 
surface area for placing connectors in the overlapped joint 
members, (2) that the members will be joined with con- 
nectors at the panel points to make it possible to take 
advantage of greater working stresses in compression due 
to the spaced column principle (see Supplement No. 4 
Wood Columns), and (3) that lateral support will be 
provided at each panel point to prevent lateral buckling 
of the top chord. 

When computing the sizes of spaced column members 
as for the top chord in question, it will usually be found 
that a large value for "d" in the l/A ratio {I = length of 
panel in inches, d^least thickness in inches) is most 
suitable up to the point where the width of the member 
becomes too narrow to permit the placement of the 
necessary number of connectors. If the value for "d" 
becomes too small, greater overlapped area results but 
the working stresses of the lumber are rapidly reduced 
and the members become inefficient and uneconomical. 

Reference to the top chord of the 50' Fink roof truss, 
Fig. 14, shows a panel length of 6' 8'74" and a maximum 
load of 38,100 lbs. With members 1%" thick, the //d 
ratio for the 6' 8%" panel length is 50; with lumber 
2%'' thick, the ratio is 31; and with lumber 3%'' thick 
the ratio is 22. Then, for lumber with a modulus of 
elasticity (E) of 1,600,000 lbs. per square inch and a 
compressive stress (c» of 880 lbs. per square inch, the 
working stresses for the different I A ratios will be 440 
lbs., 820 lbs., and 880 lbs. per square inch respectively. 
(See Supplement No. 4, page 19, curve C for Long Time 
Loads for Spaced Columns with connections located 
within //20 from the end. With c equal to 880, the 
curves on page 19 for c==9Q0 may be used since there is 
such a slight difference; no value, however, for a c=880 
grade should exceed this amount. I Dividing the 38.100 
lb. load by the values for the different //d ratios, the 
1%'' thickness requires 87 square inches, the 2%'' thick- 
ness requires 47 square inches and the 3%" thickness 
requires 43 square inches. The 1%" thickness is evi- 
dently impractical since two chord members 28" wide 
would be necessary, also chord members 3 ''is'' thick 
take only a 7^2' width to carry the load but do not 
furnish sufficient surface area to accommodate the con- 
nectors. Members 2*s" thick require a 9^ •»" face width 
to carry the load and provide sufficient overlapped area 
for placing connectors, and are therefore recommended 
for the top chord. 




^ 71/ 




"J '^ V .0,0/ 








-fnd Block 

-Spacer B/ock 

-End Block 


Diagram of Two-Member Spaced Column (Connector Joined). See 
Supplement No. 4, Spaced Columns — Safe Loads, for details cover- 
ing size anti location of connectors, end blocks and spacer blocks. 

Bottom Chord — The bottom chord member Lo, Fig. 
14, has a tension load of 35,400 lbs. Assuming a lumber 
grade of 1,200 lbs. per square inch in tension or extreme 
fibre in bending (f), 29.5 square inches of cross section 
are required. This is equivalent to approximately two 
pieces of 3" x 6" with a total net section of 29.54 sq. in. 
(See back cover of Manual.) 

Three inch thickness of members is selected primarily 
to maintain the same thic^.ness as in the top chord mem- 
bers so that the splice plates will lie flat on the faces of 
the abutting upper and lower chord members. The 6" 
width of lower chord members is sufficient to accom- 
modate the 4" split ring connectors in this joint, but 
due to the necessity of an 8" width to develop the load at 
an angle to grain in another bottom chord joint for this 
truss, the bottom chord is made 8" wide throughout its 
entire length, thereby eliminating an extra splice joint 
in the bottom chord which would otherwise be necessary. 

Web-Members — Web-members in compression can 
best be handled as solid columns, with a relatively small 
Z/d ratio, in contrast to web-members in tension, which 
may be comparatively thin since their I. A is not a factor 
in their working stresses. This combination provides for 
efficient design and a symmetrically loaded joint by plac- 
ing the compression members between the double chord 
members and the two tension members on the outside. 

Compression member V2 with a greater load than occurs 
in either VI or V3 is tentatively considered as having a 
3" thickness (2%" net) to correspond to the appropriate 
3'' thickness of the center splice plates for making splices 
in the chord members. (The thickness of the center mem- 
ber of three splice plates used for joining a two member 
chord should normally equal half the total thickness of 
the two members comprising the chord; the two outside 
splice pieces, making up the remaining necessary section.) 
Using the same 880 lb. c grade of lumber as in the top 
chord and with an l/A ratio of 25, the allowable working 
stress for member V2 is 680 lbs. per square inch. (See 
Supplement No. 4, page 19, Curve A for Long Time 
Loading of Simple Solid Columns.) The load of 7,200 
lbs. requires 10.6 square inches of cross section. A 
3'' X 6" piece with a cross section of 14.77 square inches 
will accommodate this load and provide a 6'' face for 

Assuming a 2%" net thickness for compression mem- 
bers VI and V3, Fig. 14, corresponding in thickness to 
member V2, the Z/d ratio is 12.3 for each of these two 
members. In 880 lb. c grade of lumber, this gives a 
working stress of 880 lbs. per square inch, and for the 
3,600 load, approximately four square inches of cross 
section are required. A 3" x 4" piece with a net cross 
section of 9.52 square inches is the smallest size possible, 
since the 2%'^ thickness must be maintained to fit between 
the chord members and a 3%" width of face is necessary 
for a 2y^/' split ring; therefor this member size is recom- 

Tension members D3 and D4 with a 15,000 lb. maxi- 
mum load and with the 1,200 lb. f grade of lumber used 
in the truss, will require 12.5 square inches of cross sec- 
tion. Two 2" X 6'"s with a total of 18.2 square inches 
of cross section will provide more section than necessary. 
The other tension members, Dl and D2, with a load of 
5,000 lbs. each, need less section than member D4, but 
2" X 6'"s are recommended to keep the sizes uniform 
and further because smaller structural members are not 
generally recommended. 


The order in which the joints in the Fink Truss, Fig, 
14, might logically be designed would be first the heel 
joint, because of the large loads to be transmitted, then the 
peak joint with relatively large loads and with members 
entering the joint from three directions, and finally the 
remaining joints in any order desired since they are com- 
paratively simple. However, to more clearly present the 
design principles which apply to timber connector joints, 
a few typical joints will be discussed first, and then the 
heel and peak joints of the Fink Truss, Fig. 14. 




Load Parallel to Grain 

Tension Joint— In the tension joint loaded parallel 
to grain, Fig. 15, consisting of two overlapped members 
and split rings placed in the contact faces, assume that the 
load to be carried is 14,000 lbs. and that the lumber is 
1200 lbs. f grade of Group B Species. 

Design the joint for the following conditions: 

1. Full end distances and spacings for connectors. 

2. Permissible reduced spacings. 

3. Permissible reduced end distances. 

4. Permissible reduced spacings and end distances. 

The four conditions outlined are presented to show the 
different combinations possible and how sub-standard 
spacings and distances may be computed for reduced 
loads. In actual design, it is recommended that reduc- 
tions for spacings ami distances be made on both, rather 
than on spacings or distances alone and thereby main- 
tain more uniform load reductions for all connectors. 

1. Full End DiHtances and Spacings 

Lumber Size: The 1200 lbs. f grade of lumber re- 
quires 11.7 square inches of section to carry the 14,000 
lb. load. In the table on the back cover of the Manual, 
it will be found that a 2'' x 8" member with a sectional 
area of 12.19 square inches and a 3" x 6" member with 
a sectional area of 14.77 square inches, are the smallest 
nominal lumber sizes that will carry the load in tension. 

Connector Size: Since split rings are specified for the 
joint, either one or two rows of 2^o", or 1 row of 4" 
split rings could be used in the 8" width of lumber, or 1 
row of 4'' split rings could be used in the 6" width of 
lumber. To keep the number of bolts at a minimum, 4" 
connectors are recommended, although in a structure 
where 2^*'' split rings are used in the (»ther joints, it 
may be best to use them in tliis joint also. 





Fig. 15— Two- Member TrriMon Jcint. b.adrd Parallel to Grain 

Net Section: The net sedicm of a member remaining 
after boring the boll holes and cutting the grooves must 
then be checked to determine if it is adequate: it will 
usualh be found adequate except where lumber of the 

higher stress grades is designed to nearly its full capacity. 
Checking net section is readily done by referring to the 
tables on page 15 of the Manual. In the lower table it 
will be found that the projected area of one 4" split 
ring and bolt in a member 1%'' thick is 3.09 sq. in. and 
in a member 2%'' thick is 3.84 sq. in. These values sub- 
tracted from the sectional areas of the 2" x 8" and 
3" X 6'' lumber sizes leave 9.10 sq. in. and 10.93 sq. in. 
respectively. To determine then, if the net section re- 
maining is sufficient, the actual number of square inches 
of net section required is computed from the table of 
constants, page 15, by multiplying the load to be carried 
by the constant for Standard loading for Group B Species 
in material less than 4" in thickness, which in this case 
is 14,000 X .00046, or 6.45 square inches. Therefore 
either the 2" x 8" or 3" x 6'' lumber sizes furnish ade- 
quate net section; the choice of size selected for a struc- 
ture will be determined from the design as a whole. 

Connectors Required: Working loads for split rings 
are given in the table, page 5, of the Manual. A 4" 
split ring used in one face of a member 1%" or more 
in thickness and loaded parallel to grain has a load 
capacity of 5500 lbs. for Group B Species, and to carry 
the 14.000 lb. load, 2.55 or 3 split rings are required. 
The standard spacing and end distance for these con- 
nectors for load applied parallel to grain (see Manual, 
page 4) are 9" and T respectively. With three bolts 
spaced 9" apart and a 7' end distance, the joint length 
from the end of one piece to the end of the other piece 
in the joint is T' -\- 9" -f- 9" -\- 7" or 32". 

2. Permiggibie Reduced Spacings 

Assume that it is desirable to shorten as much as pos- 
sible the spacing between bolts with 4" split rings in 
the tension joint discussed above and still carry the 
H.fKMJ lb. load. 

The total capacity of three 4" split rings is 3 x 5500 
lbs. or 16.500 lbs., but only 14.000 lbs. or 85% of their 
capar ity need be developed. Therefore, instead of the 
three connectors carrying 300% of the capacity of one 
connector, they need carry a total of only 255%. Since 
one connector in a row with reduced connector spa* ing 
is assumed to carry 100% capacity, the other two con- 
nertors need to develop 77.5% capacity for each. By 
mterpolation of spacing requirements from full spacing 
of 9" at 100% capacity to 4%" at 50% capacity, as 
givc-n in the Manual, or from the loose-leaf Spacing and 
Distance Chart No. 1 included with this booklet, the 
^pac ing may be reduced from 9" to Vk'\ The total 
joint length from the end of one member to the end 
of the other member in the joint is then 7" + 7%" + 
VVh" + 7" or 281/r'. a reduction of 33/4" from the 
length of the joint with full spacing and end disUnceg. 



3. PermisBiMe Reduced End Distance 

If the end distance only is to be reduced, the per- 
centage reduction may be applied to the end ring up 
to the maximum of 37.5% allowed, which takes the 
minimum end distance permitted. Since the permissible 
reduction for the joint is 45%, it will be seen that the 
end distance may be reduced to the minimum allowed, 
namely to 8^2" for the 4" split ring. The total joint 
length is then 3%'' for the 4" split ring. The total 
joint length is then SMj'' + 9" + 9" + 3^/' or 25". 

4. Permissible Reduced Spacing and Reduced 

En<l Distances 

In some cases it may be desirable to reduce both end 
distances and spacings. Such refluctions are made by 
iombining the two systems described under 2 and 3 
above. Assuming that the end distances are reduced, 
th*' full amount thereby reducing the capacity of the 
joint by 31.^7f, it still leaves 45% — 37.5% or 7.5% 
whirh can be applied to reduced spacing. The 7.5% 
divided by the two bolts with connectors (exclusive of 
the end bolt) gives 3.75%. By interpolation for re- 
duced sparing, the 3.75% permits the s()a( ing to be 
redu(<'d from 9" to H%'\ The total joint length would 
111*'" Ix' -^'l*" + B%" -f 8'H'' 4- 3Y/' or 24IV'. 

C]om|ireHsion Joint — A compression joint may be de- 
signed similarly to a tension joint with all the load trans- 
ferred by connectors or it may be designed with part of 
the load < arried b\ < oruiectors and [Kirl < arried b\ end 
bearing of the members with a metal plate fitted sruigly 
between them. It is frecjuently found more practical to 
design a c c>m[)ression joint with connectors carrying the 
entire lc»ad. since splice plates provide the necessary stiff- 
ness for the members joined and a minimum amount of 
labor is required to fabricate the joint. The design of the 
joint with part of the load carried b\ dirert end bearing 
offers a convenient solution, on the (»ther hand, when 
using ccunparatively large members with limited space 
for splicing and where lateral stiffness is provided by 
means other than the joint itself, such as being placed 
near or in a joint with lateral bracing. Compression 
joints in the top chords of bridge trusses offer typical 
examples where this method of designing joints is found. 
As much as KKV r of the bearing stress of the members 
may be developed b\ end bearing, provided a metal bear- 
ing plate is placed between end of members and fabrica- 
tion is accurate. Normally, however, not over 50% to 
75' ( is practical since the joint must be held together 
by some means. This is handled advantageously by 
connectors and one or more splice plates for holding 
the joint in line and for carrying a portion of the load; 
the remaining portion of the load being transferred by 

end bearing of members against a snugly fitted bearing 

Another system sometimes used is that of filling with 
concrete the space enclosed by the metal gusset plates 
and the ends of the members, the concrete forming end 
bearing for all the members entering the joint. 

The joint in the top chord member U2, Fig 14, will 
serve to explain the two design systems. Reference to 
the previous text, describing the method of finding the 
size of the top chord members, will show that the top 
chord takes two pieces of lumber 3" x 10", nominal. 
For one condition assume that the entire load of 35,100 
lbs. is carried by connectors, and for the other condition, 
that [)art of the load will be transferrt^d bv end bearing 
of the chord members. See Fig. \(k loint A arid Joint 
B respectively. 

With the entire load transmitted by splice plates, their 
cond>ined sectional area must ecjual at least the total 
sectional area of the members joined. A center |»iece 
2'm" thi( k and two side [>iece9 1%" thick provide the 
necessary section. Holli 2^j" arid l" diarnt'Jer rings 


J /o' 









^3 E 




Joint A 

J^ F I ± * ■" - r 


\ . ^'1 

Mmtat 3^artftf P/0t0s 




1 3^hcm Pfafm S J^Af P,^^ £'^4 

2 ^sfo/ B^artft^ Plotms 4 doffs ^ a 10* 

Joint B 

Fig. 16 — Details of Compression Splice with (A) Entire I^ad of 

35,100 lbs. Carried by Connectors, and ^B) 31% of the Load 

Carried by Connectors and 69r<? Carried by End Bearing af 

Members .^gain^t .Metal Plates 



will be considered since these are the most common 
sizes used in this type and size of truss. The 35,100 lbs. 
load for Group B Species requires 12.3 split rings ly^' 
in diameter each side of the joint, or 6.5 split rings 4'' 
in diameter. Twelve 2V^" split rings each side of the 
joint will safely carry the load and will fit into the joint 
conveniently. It will be necessary to use 8 split rings 
4" in diameter to keep the joint symmetrically loaded. 
The cost of labor for installation of rings of either size 
will be about equal, the single apparent advantage of 
one ring size over the other being that the 2V2'' split 
rings take slightly shorter splice plates. The joint in 
Fig. 16-A shows 4" split rings with end distances and 
spacings for full load capacity for the rings. The rings 
are placed off the center line to provide more even dis- 
tribution of load to the members. 

Fig. 16-B shows the same joint with the same load 
transmitted and member sizes as given in Fig. 16-A, 
but with bearing plates between the ends of the mem- 
bers. The outside splice plates are omitted and 214'' 
split rings are used instead of the 4" split rings. In 
this joint 31 7^^ of the load is carried by the rings and 
697o is transferred through the abutting ends of the 
compression members. 

Load at Angle to Grain 

Most structural joints have members entering at an 
angle with reference to other members and therefore 
produce bearing at an angle of load to grain. The 
several examples of joints in the following discussion 
are all of this type with each one bringing out certain 
design features. 

Chord Members Placed Between Web Members— 
This is a type of joint commonly used in ihc design 
of pitched roof trusses. By making the compression 
member the sarjie thitkness as the splice plates used be- 
tween the (h(»rd members, a comparatively low //d 
ratio is secured and furthermore, the compression mem- 
ber will also fit between the chord members. The ten- 
sion members in the joint may be thinner since their I d 
ratio is not a factor and further, since thev are placed 
outside the chord members. 

y\ joint of this type is formed bv menil>ers LI. L2. 
\2, and D3 of Fig. 14. and is detailed to larger scale in 
Fig. 3 7. 

In this joint, each of the two tension members 1)3 
exerts its load (.f 5(MM) lbs, (total 1().(XK) lbs. I at 45" to 
the grain in the two lower chord members. At this angle 
of load to grain a 4" split ring in lumber 2%" thick 
of Group B Species develops a safe working load of 
4590 lbs. Two of these rings, one between each chc»rd 
member and each diagonal, with a •'^j" bolt will develop 
9180 lbs. But this is not sufficient to carrv the 10.000 



Fig. 17— Detail Drawing for Lower Chord Joint with 4" Split 
Ring and 1" Diameter Bolt 

lb. load, and therefore to increase the load capacity 
without increasing the size of the members to accom- 
modate an extra bolt or more rings, a 1" bolt is used 
in place of the %" bolt, thereby increasing the capacity 
of the connectors by 7% (See Supplement No. 6, foot- 
note for table of split ring loads), giving a total of 
9800 lbs. This being only 2% under the full connector 
capacity required, the joint is adequate to meet good 
design requirements. Since the load in the tension 
member is acting upward at 45°, the edge distance in 
the chord member must be 3%" on the upper side of the 
ring where its outside surface is in compression against 
the wood. 

The end distance required for the 4" split ring in 
tension member D3, where the load is acting parallel to 
grain, is determined by the load it carries. The 4590 
lb. load capacity of the 4" split ring increased 7% for 
the 1" bolt, equals 4910 lbs. or 85% of the capacity of 
a ring with a one-inch bolt loaded at 0° to grain. This 
percentage capacity permits a 51/2" end distance. 

Member V2 transmits load to the lower chord at 
(ny^" to grain, at which angle the load per ring with 
a 1" boh is 4185 lbs. plus 1% or 4480 lbs., and for 
two rings is 8960 lbs. This is greater than the 7200 lbs. 
load necessary. The load in this web-member is acting 
downward so that the compression side of the ring is 
t(>ward the bottom edge of the chord, therefore this edge 
distance as well as that for the upper side must be 
3-^,", making a member with a 71/2'' face necessary. 
It is this joint in the bottom chord which requires the 
widest face width and therefore determines the width 
of the member. 

The standard end distance for a compression member 
with a 4" split ring is 51/2", but since only 80% of the 
load need be developed in member V2. the distance mav 
be reduced to 41/2". The ends of both members V2 and 
D3 ma> be sawed off parallel to the edge of the bottom 





Fig. 18 Diagonals Between Vertical and Horizontal Members 

chord about Yl' below it as shown by the dotted lines. 
Fig. 17, which still leaves sufficient end distance. 

Chord Member Placed Outside of Web-Mem- 
bers — The lower chord joint of a flat top Pratt truss 
shown in Fig. 18 has the diagonal members placed between 
the vertical and the horizontal members. Advantages 
gained by this arrangement as compared to the diagonals 
being placed outside the chord members, are that (1) the 
diagonal members which must transmit the greatest load 
have two faces into which connectors may be placed, 
whereas, if they are located outside the chord members, 
connectors could be placed in only one face of each 
diagonal; (2) the bottom chord which is in tension does 
not need to be the same thickness as the top chord to 
assemble the truss; (3) the working load per connector 
between the vertical and diagonal with a 42'' angle is 
considerably greater than it would be between the vertical 
and bottom chord with a 90° angle of load to grain. 

An analysis of the joint in Fig. 18 with axial loads in 
the members, shows that where three overlapping mem- 
bers in a joint come together at different angles, it is 
the center member with connectors in both faces which 
has the load at an angle to grain; the two side pieces 
being stressed only parallel to the grain. The side pieces 
fin this case being the horizontal chord and vertical 
web-member) must deliver their loads in the direction of 
their respective axes thereby introducing stresses in the 
diagonal piece, which combine to produce the resultant 

force equal to the load carried by the diagonal member. 
Since the compression side of the ring in one face of the 
diagonal member applies to one edge, and the compres- 
sion side of the ring in the opposite face applies to 
the opposite edge, due to the direction of loads, the 
diagonal must have a 3%" edge distance on each side 
resulting in a member with a face width of 7l/4'^ 

The vertical member in Fig. 18 with a 9100 lb. load 
to transfer to the two diagonal members at 42 degrees, 
will take two 4" split rings, one on either side, to carry 
the load, since at this angle, in Group B Species, and 
for lumber 2%" thick, one 4" ring will carry 4645 lbs. 
and two will carry 9290 lbs. The two horizontal chord 
members must transmit a total of 7700 lbs. to the diag- 
onal members (36,800-29,100) at an angle to grain of 
48°. Under the conditions presented, one ring will 
carry 4540 lbs. and two will carry 9080 lbs., which 
is more capacity than necessary to carry the 7700 lb. 
load. Therefore, since the 4'' split rings are sufficient 
to transfer the vertical and horizontal loads, they must 
also be sufficient to carry the load in the diagonal 

Heel Joint — Fink Truss — The heel joint in the Fink 
Truss shown in Fig. 14 is simplified by extending the 
top chord members to bear on the support, thereby trans- 
mitting directly to the support that portion of the load 
acting as the vertical component and eliminating the 
necessity of transferring this portion of the load by con- 
nectors through the bottom chord. (See Fig. 19.) 

In the design of the heel joint, it is apparent that 
split rings, toothed rings, claw plates or shear plates 
may be used in this timber-to-timber connection. Split 
rings, however, will be found to be most suitable since 
they carry more load than toothed rings of comparable 
size; also split rings are more easily installed than claw 
plates, no pressure being necessary to seat them; and 








CZtJ cfa 



Fig. 19 — Heel Joint of Fink Truss with Top Chord Members 
Extending to Support 



split rings are less expensive to use than either claw 
plates, or flange shear plates because 2 plates must be 
used to make a single timber-to-timber connection com- 
pared to one split ring. As previously noted it is usually 
more efficient to use the larger connector sizes since they 
keep the number of bolts and connectors at a minimum 
and facilitate fabrication. If the most appropriate con- 
nector size is not immediately evident for the joint, the 
number of connectors required for each size may then 
be computed and one selected which fits most advan- 
tageously into the members. The loads for split rings 
for the heel joint in Fig. 19 are dependent on the 22^ 
angle of load to grain bearing of the connectors in the 
top chord, on the 2%" lumber thickness as determined 
previously and on the Group B Species of lumber. It 
is assumed that the truss will be used in a location 
where the lumber will reach an air-dry condition and, 
therefore, the moisture content of the lumber need not 
be considered as influencing split ring loads. Based on 
the above conditions, the safe load for a ly^' split 
ring is 2640 lbs., for a 4" split ring the safe load is 
5005 lbs. and for a 6" split ring the safe load is 6440 lbs. 
The 35,400 lb. horizontal load which must be trans- 
ferred to the bottom chord will take 13.4 split rings 
^y*l' in diameter, 7.1 split rings 4" in diameter or 5.5 
split rings 6" in diameter. With four contacting faces 
into which connectors must be placed to keep the joint 
symmetrically loaded, the number of rings must be 
rounded off to sixteen 2^/^" rings, eight 4" rings or 
eight 6" rings. This number of rings for each size can 
be located in the heel joirit to carry the load. It will 
be noted, however, that the 4" ring size is the most 
-efficient, in that the number of connectors actuallv re- 
quired in the joint approaches nearest the number which 
is recommended for a symmetrically loaded joint. Also, 
the 4" rings take only 2 bolts and 8 connectors as com- 
pared to 4 bohs and 16 rings of the 2^^" size. If 
6" rings were used they still would require 2 bolts 
and, in addition to being less economical for this joint, 
they would be found neither necessary nor convenient 
for any other joint in the truss, therefore the 4" rings 
are recommended. A further consideration in the design 
of a joint where more than one bolt with connectors 
occur is that where the full capacity of the connectors is 
not devel(»ped as in this joint it may be desirable to 
reduce their spacings and distances. The rule for re- 
•duced spacing as discussed under **Spacing" inav be 
applied, since the full capat ities of the 4" rings are not 
developed. According to the rule the 4 rings on one 
boh will carry 400^ of one ring capacity, or 400' ^ x 
5005 lbs. = 20.020 lbs. This amount subtracted from 
35.400 lbs. leaves 15.480 lbs. for the 4 connectors on the 
second bolt or 77% of their rated load. To develop 

77 /{ load capacity, of the connectors in the second bolt, 
spacing between bolts may be reduced to T' as deter- 
mined by interpolation from design data given in the 
Manual or from the loose leaf Spacing and Distance 
Charts. End distance specified for the bottom chord 
splice plates stressed in tension parallel to grain is 7'', 
and end distance for the top chord in compression is 
51/^'' measured parallel to grain. Edge distance, since 
the angle of load to grain is less than 30 degrees, re- 
mains at the 2%'' minimum for both members and is 
provided by the members used. 

The load to be transferred between the two bottom 
chord members and the splice plates is parallel to grain, 
and for the conditions presented a 4" split ring will 
carry 5400 lbs. To carry the 35,400 lb. load, 6 rings 
are required; 8 rings, however, are recommended to 
maintain a symmetrically loaded joint. The diagonal 
cut on the end of the bottom chord member through a 
point giving a 7" standard end distance, measured along 
the center line, is not sufficient to provide the necessary 
2%" distance (equal to edge distance for 4" split ring* 
measured perpendicularly from the diagonal cut to the 
center of the boh hole. Therefore, the end distance at 
the center line must be increased. Since the edge dis- 
stance must be 2%'', the distance along the center line 
of the bottom chord is 2%" ^ sine 22'' or 7.2" 

22®\/ X^'^if Befi^0€n />Cf>^/ points 


Fig. 20— Detail of Peak Joint with 4" Split Rings and %" Bolts 

required. In practice, the end distance probably would 
be s( aled and rounded off to 7^2" or 8". Spacing of 
the connec tors mav be taken as full 9" as specified for 
full load capacity where there is sufficient area to place 
them along the chord, or the spacing may be reduced 
following the practice discussed under the Tension Joint. 
Spacing of connectors is shown as 7" in Fig. 19 to cor- 
respond to the 7' end distance of the splice. A check 
of the net section required for the members, using the 
same procedure as that explained for the Tension Joint 
will show that sufficient section is provided bv the size 
of members used. 



Peak Joint— The design of the peak joint in the Fink 
Truss, Fig. 14, demonstrates how two bohs with connectors 
may be located to accommodate three members entering 
the joint when the angle of load to grain is less than 30 
degrees, for each two contacting members. In this joint as 
detailed in Fig. 20, the 15,000 lbs. must be transferred 
from the two diagonals D4 to the two chord members U3 
and the 20,000 lbs. horizontal component must be carried 
through the splice to the other half of the truss. (This 
horizontal component is equal to the tension in the 
bottom chord at the center of the truss. See Fig. 14.) 
In this joint, connectors are located in the two over- 
lapped areas between the chord members and diagonals, 
also between chord members and the filler piece. The 
larger load of 20,000 lbs. should be considered first in the 
design of the joint, since connectors placed on the bolts 
used for the larger load will quite probably provide 
spacings and distances to develop the smaller load. Part 
of the thrust between the two half trusses could be car- 
ried by end bearing of the top chord members, in which 
case a fitting job for the metal bearing plates would be 
required. However, the two half sections of the roof 
truss must be securely attached at this joint and, regard- 
less of the means for absorbing the thrust, a splice is 
necessary and this can perform the functions of both a 
tie and a splice to carry the load. 

In the top chord members a 22° angle of load to grain 
is made by the splice piece and also by web-members 
D4. At this angle and with standard distances and spac- 
ings, the load per connector is 5005 lbs. With full 
distances and spacings therefore, 4 connectors on two 
bolts will carry the 20,000 lb. load to be transferred 
between the two chord pieces US and the filler piece. 
Since this part of the joint is in compression, the end 
distance for 4'' split rings must be 51/2''. This end 
distance for piece U3 then determines the gauge line 
for the end connector, the gauge line being parallel to 
the end cut and measured parallel with the grain in the 
chord. The required 9" spacing and 2%" edge distances 
for all members joined must also be met. In order to 
locate the two bolts with connectors within the limits 
of the diagonal D4 and still have the specified edge dis- 
tance for connectors in the chord member, it is neces- 
sary to offset the diagonal so that the intersection of the 
center lines of the diagonal and chord members is 8 
inches to the left of the panel point. The slight ex- 
centricity introduced into the joint by offsetting diagonal 
D4 is of little importance and may be neglected. The 
filler piece must be of sufficient width and length to 
provide the specified edge and end distances for con- 
nectors in that piece. A splice piece 14'' wide will pro- 
vide the necessary width and the length may be extended 
to meet the requirements. 

The four 4" split rings between the chord and web- 
members must be investigated to determine if they de- 
velop sufficient load capacity to carry the 15,000 lb. load. 
Since web-members D4 are in tension they take an end 
distance of 7" to develop full load capacity for the con- 
nectors. The spacing of connectors is the required 9'\ 
therefore, the only reduction in load capacity is that due 
to the reduced end distance from 7" to SIV' (See Fig. 
20). It will be noted that for these diagonal members, 
there are two diagonal end cuts and therefore, the end 
distance is not measured to the extreme end of the mem- 
ber but to a point a short distance from the end which 
gives approximately the required shear area for the 
connector. A reduction of P/o" in end distance reduces 
the load capacity 177o (see charts). Therefore, two con- 
nectors with full load carry 10,010 lbs. and the other 
two connectors carry 83% of 10,010 lbs. or 8310 lbs., 
which totals 18,320 lbs. or 3,320 lbs. in excess of the 
15,000 lbs. necessary to be developed. 


Combined axial and bending stresses occur in chords 
of trusses on which load is applied between panel points, 
rafters with collar beams, or columns supporting eccen- 
tric load, such as a column with an attachment for sup- 
porting a load on one side. When computing the 
stresses in members with combined loads, the resulting 
stress must necessarily be a combination of stresses due 
to each type of loading. Since the allowable tension stress 
m a timber differs from the allowable compression stress^ 
one formula is necessary for combined tension and bend- 
mg and another formula is necessary for combined com- 
pression and bending. 

Combined Axial Tension and Bending 

Allowable tension stresses and allowable bending 
stresses are the same for specific grades of lumber (See 
Supplement No. 1) and, therefore, the total allowable 
stress in the member is the sum of the two. A member 
with this type of combined loading (see Fig. 21) must 
then be designed so that the sum of the stresses must not 
exceed the bending or tension stress (f) of the grade of 
lumber used. This combination of stresses may be ex- 
pressed by the formula: 

* P^ , M must not exceed the fiber (1) 

A S stress in bending (f) 

in which 

P = Total axial load in pounds. 

A = Area in square inches of cross section of members. 
M = Total bending moment in inch pounds. 
S = Section modulus of member. 

f ^ Allowable extreme fiber stress in bending in 
pounds per square inch. 

* :?ee al^o Wi.oiJ Structural D*-<ign Data, page 4'>B, 



An example of combined tension and bending in a mem- 
ber is the bottom chord of a Fink truss when the chord is 
uniformly loaded by ceiling joists. Chord members of a 
truss are normally continuous over 2 or more panel lengths 
and consequently develop continuous beam action. In a 
continuous beam having equal spans and uniformly dis- 
tributed loading, the moment at the support next to its 
end determines the load capacity of the beam in bending. 
When the beam is continuous over three or more spans, 


this limiting moment is approximately yfT ^"^ when the 

beam is continuous over two spans or is a simple beam, 


the limiting moment is -^. Therefore, the moment which 

determines the load capacity in bending of the chord is 
usually that at the panel point next to the end of the 

^ ' r 

W/2 \A//2 

Fig. 21 — Combined Axial Tension and Bending 

three or more panels the maximum moment is -ttt* With 

truss or at a panel point near a splice; in this instance 
since we are assuming that the beam is continuous over 


10 ' 

reference to a span in which a splice occurs, it is corn- 

mon practice to use the same bending moment -r-r for 

this span also. 

For an example showing the method us^ed in determin- 
ing the stress in a member with combined tension and 
bending assume: 

Truss spacing 16 ft. on tenters 
Panel length 10 ft. 

Total live and dead load 40 lbs. per sq. ft. 
Tension in chord member 25.000 lbs 
Tentative size of chord member 5^ 2" x lPi>" 
Fiber stress in bending and in tension 1200 lbs. 
per sq. in. 

Solution : 

The adequacv of a proposed member is determined by 
computing the fiber stress (f) as follows: 
Substituting in the formula: 

P M 

-T--|- -3— must not exceed the fiber stress in bending (f 1 
\ b 

25.000 ^ ^68TO ^ ^^^ ^ ^^^^ ^ ^^^29f 






Since the total 1029f is less than the 1200 lbs. per square 
inch fiber stress for the timber grade proposed, the 
6" X 12" piece is of adequate size. 




In the design of wood columns it is customary to as- 
sume that they have pin ends even though they may be 
square cut at the ends or are continuous through points 
of lateral support. 

Columns Laterally Supported 

Lateral support as it pertains to application of the fol- 
lowing formulas implies that the member is supported 
in a direction perpendicular to the direction of the 
side load in such a manner that the dimension of the 



Fig. 22 — Combined Axial Compression and Bending 
In the Accompanying Discussion It Is Assumed that the Member 
Is Restrained from Buckling in a Direction Perpendicular to the 
Side Load. 

member in the direction of the side load (rather than 
the other cross sectional dimension) determines the 



length-breadth ( -j- 1 ratio to be used for the colu 

For rectangular columns with combined end loads, 
side loads (See Fig. 22) and eccentricity the direct com- 
pressive stress in pounds per square inch should not ex- 
ceed 'Q' computed from the formulas given herewith.* 
(Note: In the following general formulas (2) and (3), 
the effect of end loads, side loads and eccentricity are 
all (onsidered. If some of these types of loads are not 
present, some of the symbols become zero and the formu- 
las will be simplified somewhat. When there is no eccen- 
tricity 'e' in the formulas becomes zero, when side loads 
are not proportional to end loads 'k' becomes zero, and 
when side loads are proportional to end loads 's,,' be- 
comes zero. I 


f — Allowable extreme fiber stress in bending in 

pounds per square inch. 
I := Length of span or column in inches, 
dt, = Dimension of a rectangular column in the di- 
rection of the side load, 
e = Eccentricity in inc hes. 


Sh = "q- = I nit bending stress due to side load§. 



• For drriv.tion of ih#-^ f<.rmul«» »e* artirle "ForniuU* (or Columni with Side 
Loadi and EccrDtricitv* bv J. A. Newlin. SperUlitt in the Iferhanic* of Timber. 
Forest Prodoctf ULoratorv Ma.L..on Wi- and puklithed Id Buildinf Standard* 
MoBtkly. Deceaber. 1940 



k = The ratio of the unit bending stress due to side 
loads to the unit compressive stress due to end 
load when side load is proportional to end load. 

Cb :::= Allowable stress in compression parallel to the 
grain in pounds per square inch that would be 
permitted for the column if axial compression 
stress only existed, i. e., the safe working stress 

for the appropriate -y- ratio. 

Q == Allowable stress in compression parallel to grain 
in pounds per square inch that is permitted for 
the column when side and/or eccentric loads 
are combined with end loads. 

Columns with -^- 

20 or more 

Q = 

' + ^i'+'4i+^ 




Cb (f - Sb) 

Columns with 


Q = 

Cb(f - Sb) 

10 or less 

f + c.(|+k) 

Columns with -i- between 10 and 20 


= 10 and ^ = 20, using 

Assume a straight line variation of stress with -j- 


between the stress at -p 

V, 'k', and 'sb' as found for the particular member, 

but using 'cb' for -y- := 10 in the one formula and 

for - ^ 20 in the other formula, 

(Note: The formula for ~r- = 20 or more may be 


used to an — = 10 to check the adequacy of a member, 

since the values for 'Q' by this method will be somewhat 

lower than the requirement considering a straight line 

variation in stress between — = 10 and ^~ = 20). 

db db 

The values of 'e', V, and 'sb' may vary widely and 
each independent of the other. Any of them may be 
equal to zero or they may act in opposite directions. 

The loads shall, however, all be assumed to act in 
the same direction unless it can be definitely established 
that under all conditions of loading which may come 
upon the structure, they will act in opposite directions. 

Formulas for Specific Loading Conditions 

The following formulas for specific loading conditions 
are deduced from the general formulas above in accord- 
ance with the notes accompanying them. The two previ- 
ous formulas, (2) and (3), are also repeated here. 

Columns with — =: 10 or less 

Combined End and Side Load 

Cb (f-Sb) 

Q = 
Eccentrically Loaded Columns 


Q = 

Cb f 

^^ (I) 

f + 

Side Loads Proportional to End Loads 

Cb f 

Q = 

f + Cbk 

Combined End Load, Side Loads and Eccentricity 

Q = 


Cb (f - Sb) 





f + c. 


Columns with -j- = 20 or more 

Combined End and Side Load 

f + Cb 



Eccentrically Loaded 



f + Cb 1 + 



// -Cbf 

Side Loads Proportional to End Loads 
„ _ f + Cb(l + k) 

1, Side Load, 


Combined End Load, Side Load, and Eccentricity 
Q= f + <^'>ll + ^+*' 



Columns with -r- between 10 and 20 


The stress should be assumed to vary as a straight line 
between these limits as previously noted for permissible 
loads per square inch computed by the formulas for 

-r- =-- 10 or less and for -p ^ 20 or more. In practice 



since the value for 'Q' computed by the formula for 
-y- = 20 or more will be found to be only slightly less 


than the value found by a straight line interpolation be- 
tween the two formulas, it will usually be necessary to 

apply only the one formula, namely the one for — = 20 

or more. 

An example of loading w^hich introduces combined 
axial compression and side loading in a member is 
that found in the top chord of a roof truss with roof 
joists spaced between panel points. The effect of con- 
tinuous beam action over one panel point applies here 
as in the case of a member subjected to combined tension 
and bending; the bending moment being computed with 

the same formula, namely, ^tt^- With reference to a 

span in which a splice occurs, it is common practice to 


for this span also. 


use the same bending moment 

Example: f -r- =10 or less) 

As a specific example for determining the adequacy of 
the top chord member of a truss with combined compres- 
sion and bending assume the following values: 

Truss spacing, 16 ft, on centers 

Uniformly loaded top chord 

Panel length (flat roof) 10 ft. 

Total live and dead load, 40 lb. per sq. ft. 

Compression load in top chord member, 25,000 lbs. 

Tentative size of chord member, 5^^" x 13Vi>" 

Allowable fiber stress in bending, 1,200 lbs. per 
sq. inch 

Allowable compression stress, 900 lbs. per sq. inch 

Modulus of elasticity (El, 1.600,000 lbs. per sq. 


For the above conditions and with the members re- 
strained from buckling in a lateral direction in the plane 

of the roof, the -y- of the member with 'd,.* the di- 

mension of the nieml)er measured in the direction of the 

side load, is — r - oi" <^>-9. Since this ratio is less than 10. 
13 5 

and since the side load is proportional to the end l(*ad 

and further, since there is no eccentricitx . the following 

f(»rmula applies: 


Substiluling values for the symbols in the formula 

f ^ 1.2(X) lbs. per sq. inch 
V,, =: 9()0 lbs. per sq. inch ( See page 4, Supplement 
No. 4( 

k = 

M 40 X 16 X 10 X 120 
S 10 X 167.06 

P ~ 25,000 

A 74.25 


= 1.37 



900 X 1,200 

= 444 lbs. per square inch 

1,200 + 900i X 1.37 

Since the permissible computed load of 444 lbs. per sq. 
inch is greater than the actual column load of 337 lbs. 
per sq. inch as found for determining "k", the column 
is adequate. A similar check will show that a S^^" x 
] P/li" member would be inadequate. 

Example: l ^r ratio between 10 and 20) 

For an example illustrating the application of the 

formula where the -r- ratio is between 10 and 20, 


Truss spacing 12 ft. on center 

Uniformly loaded top chord 

Total live and dead load 30 lbs. per sq. ft. 

Panel length (flat roof) 12 ft. 

Compressive load of top chord 20,000 lbs. 

Tentative size of top chord S^/^'^xlP^" 

Allowable fiber stress in bending f 1,200 lbs. per 

sq. ft. 
Allowable compressive stress c 900 lbs. per sq. inch 
Modulus of elasticity E 1,600,000 lbs. per sq. inch 
Top chord is restrained laterally. 

Solution : 

The ^ ratio of the member with 'd,,' the dimension 

of the side of the member measured in the direction of 


the side load is yy^ or 12.5; this being a ratio between 

10 and 20 with side loads proportional to end loads, 
and no eccentricity the two following formulas apply 
with a straight line interpolation between the two re- 
sults secured to give the permissible unit safe loads. 

f + Cb(l+k) 

= 20 or more 



. / jf + Cb (1 

V \ 2 

+ k)C^ 

= 10 or less 


f + Cbk 

Cbf (9) 


If it is found by substituting in formula (9) that the 
load capacity de\ eloped in the member is sufficient to 
meet the requirements, no further computations are 



necessary. However, if the capacity of the member is 
slightly lower than that required, it may then be desira- 
ble to compute the stresses by each of the formulas 

-T- = 20 or more and -^ = 10 or less and then de- 
db clb 

termine the stress by a straight line ratio as explained 
previously. The stress thus determined will be slightly 
greater than that determined by formula 1 9 ) and may be 
sufficient to develop the necessary load. If this new 
stress is still insufficient, it then becomes necessary to 
investigate a larger sized member. 

Substituting values for the symbols in the formula (9) : 
f = 1,200 lbs. per sq. inch 

Cb = 887 lbs. per sq. inch (See page 4 Supplement 
No. 4) 

k = 

M 30 X 12 X 12 X 144 

S ^ 10 X 121.23 

P_ 20;00Q 

A 63.25 


- 1.63 


Q = 

1,200 + 887(1 + 1.63) 


1,200 + 8870 + 1^ r- 

= 1,765 - 1431 

2 7 

334 lbs per sq. inch 

- 887 X 1,200 

Since the permissible end load stress is 334 lbs. per sq. 
inch and only 315 lbs. per sq. inch need be developed, 
the member is, therefore, of adequate size. 


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f ~. ~ 

JLumbct and ^onnectot Jlitetatute 

TiiiibtT Engineering Company, 

Kiiiziiurrin^ in Tiinher. A 24-page pictorial and dejscriptive 
prr^entation of Teto tiniljer j-lrurlures. Free. 

The Manual of Timber (Connector Construction. A 16-page 
hnllctin giving tcclinital data on Tcco connectors. This Manual 
((►ntains (onipltte inf(>rniation for the use of engineers in design- 
ing wood struct ures. Data are iiased on test inf<»rmalion obtained 
from 11. S. Forest Products Laborator>. Free. 

Typical Lumlter Designs. A bulletin listing 100 typical de- 
signs for various Iyi>es of light and heavy frame structures, 
[designs include quantities and materials lists. P>ee. 

Railway Timber Structures. 8 i)ages. Details (»f tyjtical rail- 
way Uses for Teco limber connectors. Free. 

M(Mlern Timber Highway Bridges. 16 pages. Twelve bridge 
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Reprints from various trade magazines describing many types 
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Instructions for use and care <»f Teco Grooving and Dapping 
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Instructions for Installing Teco Toothed Ring Connectors with 
High Strength Rod and Ball Bearing \^ asher. Free. 

Packing Plants, Economical Market Sheds, and \^arehouses use 
Timber Connector C<mstruction. A pict(»rial booklet shc»wing 
several types of roof trusses and methods u{ fabrication and 
erection. Free. 

Installing Teco Timber Connectors in Light and Heavy Struc- 
tures. Pictorial btmklet showing fundamental procedure for in- 
stalling Connector"* in timber i<tints. Free. 

National Lunibf*r Manufacturers A»«>n.« 

Wood Structural Design Data is a 300-page book published by 
The National Lumber Manufacturers Association. It contains 
complete tables of safe loads for wood joists beams and columns 

Prinifd in U.S.A. 
12 M-rSM 

c(jvering the full range of commercial sizes, species and grades, 
and of the spans and heights ordinarily used. The book contains 
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useful to designers. Price $1.00 \wt copy; with foll.»viir»g su[>|)le- 
ments $1.25, U. S. postage paid. 

Wood Structural Design Data .Supplements: 

Supplement 1 -Working Stresses f(»r Structural Lumlter and 

Supplement 2 
Supplement 3 
Supplement 4 
Supplement 5 

Bolt»'d Wood Joints safe loads. 

-Maximum Spans f(»r J(»ist>- and Rafter'-. 

Vi'ood (>)lumns -safe load". 

Wood Trusses — stress coef^n irui^, b-ngth ( 
efficients and angles. 
Supplement 6 Manual of Timber Connector (.onstrurt irui. 
Supplement 7 Stud Walls safe axial loads. 

Lumber (irade-Lse (iuide. published by National Lumber Manu- 
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Stronger Frame ^Xalls. How wood walls should be framed 
for p-eatest strength. Based on lalK»ratory tests. (10r» 

Airplane Hangar (>>nstruction The advantages and uses of 
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sample plan*-. < lOcI 

Pictorial Review of Hangar Fire Tests. UOc) 

Exposing the Termite Booklet giving brief history of the 
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methods of preventing termite attack. Free.